The objective of the Zoster Eye Disease Study (ZEDS) is to determine whether prolonged suppressive oral antiviral treatment with valacyclovir reduces complications of Herpes Zoster Ophthalmicus (HZO), thereby improving clinical outcomes in this common and potentially vision- and life-threatening disease. There are 1,000,000 new cases of Herpes Zoster (HZ) per year in the USA, with 10-20% being HZO. The first aim of this double-masked, placebo controlled multicenter randomized clinical trial will test the hypothesis that suppressive antiviral treatment for 12 months with oral valacyclovir 1000 mg daily reduces the rate of new or worsening dendriform epithelial keratitis, stromal keratitis, endothelial keratitis or uveitis compared to placebo, at 12 months as the primary endpoint, and at 18 months including 6 months of follow-up after treatment, as the secondary endpoint, in patients with HZO who have had an episode of one of these disease manifestations during the year prior to enrollment. The second aim is to test the hypothesis that suppressive treatment for 12 months with oral valacyclovir 1000 mg daily reduces the severity and duration of postherpetic neuralgia (PHN), compared to placebo, at 12 months and at 18 months as secondary endpoints, in similar patients with HZO. PHN is a debilitating chronic pain syndrome that negatively impacts quality of life, especially in elderly patients. The study will enroll immunocompetent patients age 18 years and older who have HZO diagnosed at variable times in the past, with these types of active anterior segment ocular segment disease within the past year. Eligible patients will be randomized in a 1:1 ratio to long-term suppressive treatment with oral valacyclovir 1000 mg daily or placebo for 12 months, plus usual ophthalmic care, and followed every 3 months for a total of 18 months, to determine outcomes of new or worsening dendriform epithelial keratitis, stromal keratitis, endothelial keratitis or uveitis and/or severity and duration of PHN during 12 months of treatment and for 6 months following treatment discontinuation. The results with regard to PHN may be applicable to HZ in other locations. If suppressive valacyclovir treatment is determined to be effective, the potentially devastating disease burden of HZO and HZ may be reduced for patients, as well as the annual costs to society, estimated in the USA to be one billion dollars.